From an environmental contaminant standpoint, halocarbons can present a number of ecological and health problems. These materials are therefore of significant concern from a biological standpoint. The term “halocarbon” as used herein shall encompass a compound having at least one carbon atom and at least one halogen atom. Of considerable importance within the general class of halocarbons discussed above are halogenated hydrocarbon materials (both of the aliphatic and aromatic variety). Halogens include the following chemical elements: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). Hydrocarbons traditionally encompass those materials which are constituted of only carbon and hydrogen. A combination of both materials (e.g. hydrocarbons+halogens) will result in the creation of halogenated hydrocarbons which, as noted above, are frequently capable of producing undesirable environmental effects and adverse health conditions. However, as will be discussed in considerable detail below, the present invention is applicable to all types of halocarbons whether or not they involve halogenated hydrocarbons. For example, in addition to encompassing halogenated hydrocarbons as previously noted, the term “halocarbon” as used in discussing the claimed processes shall also encompass without limitation perhalogenated materials and other halogenated organic compositions which are not hydrocarbons or halogenated hydrocarbons (for example, carbon tetrachloride and the like).
Halocarbons are typically generated in a variety of industrial processes including those associated with electronic component fabrication, dielectric applications, metal finishing procedures, paint production, plastics fabrication/recycling, oil manufacture, and other commercial activities. Representative halocarbons of particular concern include but are not limited to polyhalogenated aromatic and polyhalogenated polyaromatic compounds (for example, polychlorinated biphenyls), as well as aliphatic halides (e.g. polyhalogenated ethylene, chloroform, carbon tetrachloride, methylene chloride, and others without limitation).
A variety of disposal and destruction techniques have been investigated for the purpose of eliminating halocarbon compositions (with the terms “halocarbon”, “halocarbon composition”, “halocarbon material”, and “halocarbon compound” being considered equivalent and used interchangeably herein). These methods include, for instance, burial at designated waste sites, incineration, photodecomposition, adsorption, and chemical degradation. One method of particular interest which has been extensively studied is the incineration of halocarbon waste compounds. However, a number of difficulties and disadvantages exist regarding this approach. For example, the incineration of halocarbons can yield additional hazardous airborne contaminants which are ultimately dispersed over a wide geographic area. Incineration processes likewise require high-temperature conditions and are therefore energy-intensive. Also of concern in the implementation of incineration procedures are the significant costs which are necessarily incurred in fabricating and operating large-scale incineration systems. Likewise, these techniques often function in a fairly slow manner, thereby creating a storage problem situation when large quantities of halocarbon compounds need to be incinerated.
Other techniques which have been developed for the destruction of halocarbons include the addition of alkaline solutions thereto as outlined in U.S. Pat. No. 4,351,978. In this patent, a procedure is described wherein alkaline compositions are combined with, for instance, polychlorinated biphenyls (PCBs) and alcohol dispersing agents. The foregoing technique (which employs Raney-type catalysts) requires the establishment and maintenance of controlled alkaline conditions in order to sustain the reactive capabilities of the chosen catalyst(s). It also requires the addition of gaseous hydrogen (H2) in order to properly implement the necessary halogen-hydrogen substitution reactions which are needed for effective dehalogenation. Another technique for destroying halocarbons (disclosed in U.S. Pat. No. 4,931,167) requires the use of Lewis acid catalysts under anhydrous conditions at temperatures in excess of 300° C. Factors to be considered in the foregoing procedures (and others) include the employment of costly and potentially-reactive (e.g. dangerous) reagents in the destruction process and the hazards associated therewith.
Additional dehalogenation/destruction techniques and/or related technologies are disclosed in, for example, U.S. Pat. Nos. 4,806,514; 4,950,833; 5,043,054; 5,141,629; 5,174,893; 5,185,488; 5,369,214; 5,490,919; 5,780,669; and 5,994,604. Notwithstanding the processes discussed above and incorporated within the foregoing references, the present invention offers a considerable advance in the art of halocarbon destruction. The claimed procedures provide numerous benefits which, particularly from a collective standpoint, had not been achieved prior to the present invention. In this regard, the processes described below satisfy a long-felt need for a dehalogenation method which accomplishes the following benefits and goals simultaneously (with the foregoing list not being considered exhaustive): (1) improved reaction rates; (2) more advantageous material transport characteristics (e.g. favorable “mass transport” properties) resulting in the rapid and efficient production of dehalogenated products; (3) the ability to avoid generating large quantities of additional toxic materials as reaction by-products; (4) a high level of versatility with particular reference to the types of compositions that can be dehalogenated; (5) reduced production facility costs compared with, for instance, incineration systems; (6) the elimination of high-temperature combustive reactors and the energy requirements associated therewith; (7) the ability to accomplish complete destruction of the desired halogenated compounds without requiring highly reactive (e.g. dangerous) reducing agents and other comparable materials; (8) the further ability to employ low-cost and safer reactants; (9) the implementation of processes which are cost effective, readily controllable (e.g. customizable on-demand), easily scaled up or down as needed, and capable of rapid integration with other processing systems including those used for extraction and separation of reaction products; (10) greater catalyst life; (11) enhanced and improved catalyst cleaning characteristics; (12) more advantageous reaction kinetics; (13) the ability in certain situations to recycle reaction products back into the system for use as reactants and in various related applications; and other benefits.
As outlined above, the claimed processes are characterized by a multitude of specific benefits in combination. These benefits include but are not limited to items (1)–(13) recited above both on an individual and simultaneous basis which are attainable in a substantially automatic manner (with the simultaneous achievement of such goals being of particular importance and novelty). The attainment of these objectives is especially important regarding the following specific items: a high reaction rate, improved mass transport characteristics, lower overall temperature requirements, greater system versatility/controllability, better safety, enhanced catalyst cleaning capabilities, and improved overall efficiency compared with previous destruction techniques. The catalytic dehalogenation procedures set forth herein and in the various embodiments associated therewith perform all of the functions mentioned above in a uniquely effective and simultaneous manner while using a minimal number of reactants, equipment, labor, and operational requirements. As a result, dehalogenation processes of minimal complexity and high effectiveness are created that nonetheless exhibit a substantial number of beneficial attributes in an unexpectedly efficient fashion. In this regard, the developments disclosed herein represent an important advance in waste treatment technology (with particular reference to halocarbons). Specific information concerning the novel process steps and reaction conditions associated therewith (which, in particular, constitute a substantial departure from prior methods) will be presented below in the following Summary, Brief Description of the Drawing, and Detailed Description sections.